Demonstrates how BTree parameters affects performance. BTreeMap has two key parameters
which affects its performance:

Maximal node size

Controls how but BTree node can get, before it splits.
All keys and values in BTree node are stored and deserialized together.
Large nodes means fewer disk access (tree structure is shallower),
but also more data to read (more keys to be deserialized).

Store values inside node

Value may be stored inside or outside of BTree node.
It is recommended to store large values outside nodes.